We currently lack knowledge on the intermediary mechanisms whereby lead exposure translates itself into increased behavior problems in childhood. This K02 Independent Scientist Development Award application will enable the candidate to develop an interdisciplinary program of research whose overarching goal is to uncover the cognitive and affective mechanisms of action underlying lead exposure-behavior problems relationship in a large sample of community children. This research program questions the current CDC "safe" standard of 10 ug/dl of lead, and hypothesizes that early sub-clinical lead exposure results in negative clinical, cognitive, and affective functioning. Building on an NIEHS-funded community preschool cohort study, the investigators will first propose to repeat measurements of both blood lead levels and behavioral outcomes to assess whether children with sustained sub-clinical blood lead levels across time are especially likely to develop externalizing behavior problems. Second, the investigators aim to understand how lead exposure interacts with social risk factors in predisposing to externalizing behavior problems. Third, and importantly, they propose to elucidate the neurocognitive and affective mediating mechanisms by which lead exposure during the preschool years contribute to externalizing behavior problems in early adolescence. This K02 will help foster the candidate's ability to achieve these research goals by providing her with protected time to collaborate more closely with senior scientists in the field, to be more fully engaged in her NIH- funded international research project on this sample, and to enhance her interdisciplinary knowledge and skills in development psychopathology, environmental toxicity, psycho-physiological testing, and advanced statistical analysis. Programmatically, the K02 will be of critical value in moving her into a new line of interdisciplinary research on prevention and intervention of behavior problems by giving her time to develop a nutritional intervention for preventing and treating behavior problems in lead-exposed children. This research program consequently has the potential to help redefine what level of lead exposure is safe, identify hitherto unknown mechanisms of action, and reduce childhood behavior problems throughout the community.